The present invention relates to a press in a machine for production or treatment of a continuously running web of cellulosic fibrous material, for instance a paper, tissue or board machine, which press comprises a press device and a counter element arranged opposite the press device, which is arranged to form a press zone in the form of an extended press nip in cooperation with the press device having a certain width in the machine direction W for pressing the fibrous web as it runs through the press nip, which press device comprises
a press shoe;
a support element for supporting and pressing the press shoe in direction towards the counter element via
at least one power device arranged between the press shoe and the support element for application of a certain pressure onto the fibrous web at the pressing operation;
a flexible and preferably impermeable belt that is arranged to run in a continuous loop around the support element and through the press nip having a sliding contact with the press shoe; and
a first guide for the press shoe arranged downstream of the press shoe, which first guide is movable between at least a first and a second position.
The present invention also relates to a method for altering the pressure profile in a press in a machine in which a continuously running web of cellulosic fibrous material is produced or is treated, for instance a paper, tissue or board machine, which press comprises a press device and a counter element arranged opposite the press device, which forms a press zone in the form of an extended press nip in cooperation with the press device having a certain width in the machine direction W so that a pressing of the fibrous web occurs during the passage through the press nip, which press device comprises
a press shoe;
a support element that supports and press the press shoe in direction towards the counter element via
at least one power device which is arranged between the press shoe and the support element and which power device is applying a certain pressure onto the fibrous web during the pressing operation;
a flexible and preferably impermeable belt that runs in a continuous loop around the support element and through the press nip having a sliding contact with the press shoe, and a first guide for the press shoe arranged downstream of the press shoe and which first guide is transferred by dismounting and/or adjustment between at least a first and a second position.
Presses of above specified type are known in different designs and have since long ago been used in production of different paper and cardboard grades, especially for wet pressing with the intention to raise the dry solids content of the fibrous web, but may also be used for calendering with the intention to improve surface properties or other physical properties of the web. Typically for presses that comprise press devices having an extended press nip and which presses and press devices usually are named shoe presses and shoe press rolls respectively, is that they provide a plurality of advantages through their longer press nips compared with presses having a conventional press nip. The expression xe2x80x9ca conventional press nipxe2x80x9d implies in this context, a press nip in which two rigid rolls, having cylindrical cross-section, are cooperating with each other under pressure. However, the dwell time for the fibrous web in this type of press nip is only some few milliseconds because of the short press nip. In a shoe press, wherein the press nip normally is extended to approximately 20 to 30 cm, the dwell time, during which the wet fibrous web is exposed to a pressure, is considerably longer, which results in much higher water flows from the web. Additional advantages, which are achieved in comparison with presses having a conventional press nip and in which, also unlike shoe presses, an effective nip pressure can be obtained only in the press direction, are a higher dry solids content of the web at the same nip pressure, or a more lenient pressing for the web at a lower nip pressure with maintained dry solids content of the web. The latter is especially essential in the manufacture of tissue where a high pressure results in unwanted tissue properties. In the case of production of tissue, which has a low basis weight and which is used for production of household paper, for instance paper towels and other hygiene products, it is important that the bulk, i.e. the relationship between the volume and the weight of the paper, is high because high bulk paper has a desirable combination of softness and high absorption power.
However, it is also of great importance for the final properties of the fibrous web in question that the pressure in the nip is not just regulated in the press direction but also that the nip pressure in the machine direction and across this may be distributed in a suitable way within the press zone between the press shoe and the counter element, i.e. that a certain and defined pressure profile is maintained in every longitudinal section and cross-section within said press zone.
It is known, for instance through the American patent U.S. Pat. No. 4,713,147, see the FIGS. 2, 5 and 6, to successively arrange several independently working arrangements of power devices in the machine direction between the press shoe and a fixed support element for these power devices to try to achieve a suitable distribution of pressure within the press zone between the press shoe and the counter element for the fibrous web in question. Each individual power device arrangement extends across the fibrous web and is thereby so arranged that it is working in the press direction towards the press shoe and thereby also towards the counter element having the fibrous web pressed there between. Then, by varying the pressure from each power device relative to the other power devices, seen in the machine direction, the position for the common pressure resultant force is transferred towards the press shoe in either the downstream or upstream direction and thereby also the distribution of pressure within the press zone. Through the same document, it is also known to alter the position for said pressure resultant force by means of a power device displaceable in the machine direction.
Consequently, all changes of the pressure profile must be done by shifting the configurations of the entire position of the actual power device arrangement in question and/or by adjusting the loads that are loaded against the press shoe by separate transverse rows of power devices, which configurations and/or adjustments first thereafter provide the desired alterations of the pressure profile by a small pivoting in the machine direction of an otherwise entirely fixed press shoe. However, it is desirable that the pressure profile may be set without transferring or adjusting the power device arrangement as an entity, while this is complicated both in a mechanical and control engineering way and which therefore is unfavorable, but which also means an essential change of the actual torque that the support element must endure.
In relation to I-beams, box girders have a higher torsional rigidity but they also have certain disadvantages. For instance, the assembly may become more complicated, which in its turn may make the shoe press construction more expensive. It is therefore desirable to find a shoe press construction that enables the use of an I-beam support element and in which shoe press construction the pressure profile may be changed without any risk for pivoting of said I-beam support element.
For instance, through the European patent application EP-A1-0 345 500 a press is known, in which several power devices are arranged as above, i.e. successively in the machine direction between the press shoe and a fixed support for the power devices, but which power devices each also comprises several press cylinders arranged in a row across the fibrous web and by which the distribution of pressure across the machine direction may be regulated by varying the pressure in each press cylinder across the fibrous web.
It is understood, that when the position of the press shoe is changed in the upstream or downstream direction in relation to a counter roll having a certain radius, a simultaneous and required angular adjustment must occur around the longitudinal axis of the press shoe that adjusts the cooperating sliding surfaces of the press shoe and the counter roll relative each other. The same thing goes for a press device having several rows of power devices arranged successively in the machine direction, in which an angular adjustment of the press shoe is desired in order to achieve an increase or a reduction of the nip pressure profile in the machine direction and which is achieved by the different magnitudes of the pressures which are applied on the press shoe from the downstream and the upstream located row of power devices. However, it is also understood that a limited expansion, displacement, pivoting and/or angular adjustment of the press shoe in relation to a horizontal plane in the cross machine direction is feasible since the power devices are not entirely fixed at the press shoe and the support element. This mobility must, however, be within certain determined limits, or problems with the pressure profile and/or damages or needless wear on the integral construction parts will arise.
Consequently, it is very important, in addition to the absorbing of the frictional forces generated in the machine direction during operation, to guide and support the shoe in all directions so that it only may deviate from its intended position within certain, very precisely determined limits.
Therefore, the shoe press known through EP-A1-0 345 500 comprises a strong support element that is fixedly mounted across the machine direction at the support element of the shoe press roll and downstream of the press nip, and against which support the press shoe is in loose contact for obtaining of the wanted support and guiding of the same. The European patent application EP-A2-0 933 471 shows an additional example of a known shoe press, which comprises a fixed support that is arranged downstream of the press shoe and across the.cross machine direction for absorbing and preventing unwanted horizontal forces and movements outwards in the machine direction. The shoe press also comprises additional guides and supports, which also are supposed to limit or prevent unwanted movements in the upstream direction and across the machine direction. Consequently, a front guide, which is directed forwardly in the machine direction is arranged in the middle of the press shoe and two side guides are arranged with one guide at each end part of the press shoe. Each side guide has a projection that projects from the press shoe across the machine direction. The front guide is cooperating with the fixed support located downstream for limiting movements across the machine direction and the two projections of the side guides are cooperating with two fixed stops for limiting movements in the upstream direction of the press shoe and for preventing an angular adjustment of the press shoe in relation to an axis across said machine direction, i.e. that one side of the shoe is situated more upstream than that of the opposed side.
Also the shoe press shown in EP-A2-0 933 471 has an entirely fixed support for the press shoe, and therefore also the position of the press shoe is entirely fixed in relation to the counter roll. The change of the pressure profile is done exclusively by changes in or of the position of the power devices so that the press shoe in its turn is pivoted around its own longitudinal axis. No displacement of the press shoe occurs in the horizontal plane, i.e. in the web feed direction.
The alteration of the pressure profile is done by mounting different strips, having varying cross-section dimensions, across the machine direction to the upstream and downstream longitudinal sides of the press shoe and/or of the power device, whereby the position of the power device may be altered in relation to the still fixedly arranged supports and stops by moving the upstream mounted strip from a position along the upstream side of the press shoe to a position at the downstream side of the press shoe and vice versa for the strip mounted downstream. The two strips have different cross-section dimensions, and therefore the power device is moved both in relation to the support element and to the press shoe whereby the pressure profile thus will be changed.
Accordingly, in all the shoe presses described above, the supports and the guides for the press shoe are fixed, i.e. entirely immovable, and all maneuvering operations, i.e. all controlled changes in the position of the press shoe and hence the pressure profile, is effected exclusively by changes in or of the position of the power devices so that the press shoe in its turn is pivoted around its own longitudinal axis. In the horizontal plane, i.e. the feed direction of the web, no displacement of the press shoe is done. As already mentioned above, the displacement of the entire or of essential parts of the power device in relation to the support element and the press shoe enforces an unnecessarily complicated and expensive construction.
Finally, a shoe press is known through U.S. Pat. No. 5,676,799, wherein a movable downstream support has been arranged for the press shoe and in which it is indicated that the pressure profile may be influenced by positioning of the press shoe.
However, the shown shoe press comprises only one guide that is arranged downstream, and therefore only the horizontal forces and movements in the machine direction may be controlled. Furthermore, the stop lacks an accurate and exact arrangement for adjusting its position in the machine direction.
The press devices in the described presses are, in addition to the imperfections during operation mentioned above, also proportionately complicated to manufacture, to install and to dismount at service or when changing press devices.
The object of the present invention is to provide a press having a substantially improved press device, which press device has guides and supports that functions in a considerably better way than earlier and also in all directions necessary, which is uncomplicated to manufacture having low production costs as a consequence, which is simple to assemble and dismount in case of servicing or changing and which press device works in a satisfying way also when an I-beam support element is being used.
According to the invention, the press is characterized in that the press device further comprises a second guide for the press shoe arranged substantially upstream of the press shoe or at least is functioning from the upstream side of the press shoe and substantially in the machine direction W and which second guide is movable between at least a first. and a second position.
According to additional aspects for a press according to the invention, it is applicable:
that the first guide for the press shoe is arranged in a dismountable and adjustable way and comprises at least one support and at least one spacing member;
that each support and spacing member is manufactured in the form of a profiled rail that extends along the press shoe;
that the support comprises two parts, which consist of a lower assembly part and an upper contact part, against which contact part the press shoe is in contact with its long side facing downstream;
that the support is arranged in a displaceable manner in relation to the support element and to the power device by means of elongated, through-going grooves arranged in the assembly part, which grooves extend parallel to each other in the machine direction;
that the support is screwed tightly but releasably to the support element by means of screws arranged in the grooves;
that the spacing member comprises several different part members having different and predetermined widths for obtaining a predetermined and adjustable position for the upper contact part against the press shoe and thereby also for variation of the position of the press shoe in relation to the integrated power devices;
that the second guide for the press shoe comprises two lateral supports, which are arranged in a dismountable and displaceable way at the cross ends of the press shoe;
that the lateral supports are displaceable in an infinitely variable way by means of fasteners and elongated, through-going grooves, which extend successively in a straight line in the machine direction, between at least two positions which are predetermined and fixed by the fasteners and the grooves;
that each lateral support comprises a lower assembly part for mounting of the lateral support to the support element and an upper contact part having a preferably vertical contact surface facing downstream for an upstream guide of the press shoe;
that the press shoe comprises a fixed projection at each of its two cross ends, and with which two projections the contact parts are arranged to be in contact, each having a contact surface of its own;
that the second guide for the press shoe comprises two lateral supports, which lateral supports are fixed at the cross ends of the press shoe in a dismountable and turnable way by means of fasteners;
that each lateral support comprises a lower assembly part for assembling the lateral support to the support element and two upper contact parts being arranged at different distances from the center of the lateral support;
that the upper contact parts each comprises a preferably vertical contact surface that is facing the other contact surface;
that the press shoe comprises two affixed projections, one at each of its cross ends, and against which projections the contact surface of the most upstream positioned contact part is arranged to bear on for an upstream guide of the press shoe;
that the press shoe comprises an eccentric in the form of an eccentrically, pivotable projection arranged at each of the cross ends of the press shoe;
that the spacing member is arranged in a turnable or pivotable way;
that said power devices comprise a number of press cylinders, which are arranged along the press shoe in a straight line and at a certain distance from each other;
that the press shoe is arranged freely resting onto the upper piston ends of the press cylinders for obtaining said free mobility in all directions;
that the second guide consists of a similar, but reversed, guide as the first guide arranged downstream, and which second guide is arranged in a dismountable and adjustable way at several predetermined and fixed positions against and in relation to the first guide;
that the press device is aligned across the machine direction W;
that the counter element comprises a rotatably journalled counter roll that is substantially parallel with the press device;
that the support element for supporting the press shoe consists of an I-beam having a substantially flat waist;
that the resultant force F of the power device arrangement is arranged to work in alignment with the center plane of the waist; and
that the press shoe extends in one single piece across the entire belt and that a friction-absorbing layer of hydraulic fluid having a certain hydrokinetic pressure is arranged between the press shoe and the belt.
The method according to the invention is characterized in that a second guide for the press shoe, which is arranged substantially upstream of the press shoe or at least on the upstream side of the press shoe, is acting substantially in the machine direction W and which second guide is transferred between at least a first and a second position by being dismounted and/or adjusted.